In universally known CMP apparatuses (Japanese Patent Application Kokai No. H6-21028, Japanese Patent Application Kokai No. H7-266219, Japanese Patent Application Kokai No. H8-192353, Japanese Patent Application Kokai No. H8-293477, Japanese Patent Application Kokai No. H10-173715, Japanese Patent Application Kokai No. H11-156711 and British Laid-Open Patent No. 2331948, etc.), an object of polishing is polished by supporting a surface plate on which a polishing pad is pasted on a spindle shaft, causing this surface plate to rotate, rotating the object of polishing that is held on a chuck that faces this, pressing the object of polishing that is held on a chuck against the surface of the polishing pad while supplying a polishing agent (slurry) to this surface, causing the pad and object of polishing to rotate in the same direction or in opposite directions in relative terms, and swinging the polishing pad.
Polishing pad materials that are used include hard foam urethane sheets, polyester fiber nonwoven fabrics, felt, polyvinyl alcohol fiber nonwoven fabrics, nylon fiber nonwoven fabrics, and materials in which a foaming urethane resin solution is flow-spread on such nonwoven fabrics, and is then foamed and hardened, etc.
Conventionally, the polishing pad shape has been circular, like the shape of the substrate that is being polished, and pads with a thickness of 3 to 7 mm have been used in a configuration in which these pads are pasted to a surface plate such as an aluminum plate or stainless steel plate.
Furthermore, pads that are larger than the object of polishing have been used as polishing pads in the past; however, for reasons such as the difficulty in uniform polishing caused by the increased difference between the peripheral speed in the outer portion and the peripheral speed in the central portion, and the difficulty in high-speed rotation of a surface plate that has large dimensions, so-called small-diameter pads, which have a smaller size than that of an object of polishing, have come to be used recently.
Generally, a Preston's equation such as the one shown below is used as an equation for determining the amount of polishing:V=n·P·v·tHere, V is the polishing speed, n is a constant, P is the contact pressure of the polishing pad and object of polishing, v is the relative linear velocity of the polishing pad and object of polishing, and t is the contact time of the polishing pad and object of polishing. In order to perform uniform polishing, the polishing speed determined by V must be more or less the same at each point of the object of polishing.
In the case of a polishing system using a small-diameter pad, a portion of the object of polishing is polished at any given moment, so that a polishing method is used under swing conditions in which the polishing pad overhangs from the object of polishing in order to ensure high-speed polishing and polishing uniformity.
However, when the polishing pad overhangs from the object of polishing, the contact area between the polishing pad and object of polishing fluctuates due to swinging, so that the load per unit area fluctuates. Furthermore, in cases where the diaphragm system of a pressure mechanism is used, inclination of the polishing pad and fluctuation of the load occur due to the overhang from the object of polishing. As a result, the product of the integrated value of the load and the integrated value of the relative linear velocity during the polishing time does not show the same value at various points within the surface of the object of polishing. In other words, polishing is performed unevenly.
Therefore, to keep this value the same, a method is employed in which the swing speed is varied according to the swing position (adjustment is made according to the contact time between the object of polishing and polishing pad), or the load is controlled so as to be constant.
[Problems to be Solved by the Invention]
However, in cases where the swing speed is varied according to the swing position, the following problems are encountered: specifically, the conditions of varying the speed to achieve the uniform polishing become complex, and the machinery cannot catch up with the command speed determined. Furthermore, in cases where the pressure is controlled according to the swing position so that the load per unit area is constant, the problem is that there may be delay in control due to the compression of the fluid, etc., used for pressurization. Because of these problems, it is difficult to uniformly polish objects of polishing in a polishing apparatus using a small-diameter pad.